An experimental investigation is presented of the foam separation of cyanide complexed with ferrous iron, using a cationic surfactant, ethylhexadecyldimethylammonium bromide. With a 25 min. foaming time, an initial iron to total cyanide ratio of 0·351:1 and an initial surfactant to complexed cyanide ratio of about 0·34:1 suspensions containing from 1·54 to 3·08 mM total cyanide can be reduced to about 0·11 mM in complexed cyanide and 0·29 mM in non‐complexed cyanide.
The rate of surfactant removal was satisfied by a first‐order relationship, similar to that obtained with colloidal ferric oxide. The rate of complexed cyanide removal was satisfied by a reversible, approximately first‐order relationship eliminating the residual surfactant concentration. The pulsed addition of surfactant in three dosages during the course of an experiment, compared with a single dose at the beginning of an experiment, produced lower residual concentrations of complexed cyanide and higher foam volumes. At an iron to total cyanide ratio of 0·351:1,90% of the complexed cyanide concentration could be removed by one fifth less surfactant, using pulsed addition, compared with a single dose.